HELP with postinstall script

i want to postinstall script in ksh. but it seems postinstall script runs only in "sh". commands like set -A (for arrays) which are perfectly acceptable in ksh gives an error when run on postinstall script even when i give ksh as interpreter.
So is it like postinstall script in solaris packaging always run in "sh"???

create a ksh script and call it in the postinstall script.